Abstract

Liebherr develops air systems, which can include low transonic, low pressure ratio, and low solidity axial fan. The operating range for such a fan needs to be as wide as possible. Thus, the goal of this study is an improvement of stall margin without performance modification. The literature reported the favourable effects of low tip clearance, blade sweep or casing treatment on stall margin for highly loaded, low speed fan. These technological solutions are carried out on Liebherr fans. The tip vortex trajectory is deflected towards the suction side as the casing is treated and reaches the leading edge of the adjacent blade for lower mass flow. On the contrary, the rolling-up seems to be independent of the mass flow when the tip clearance is small or the blade is skewed, and the strongly deviated flow spills onto the leading edge of the adjacent blade for lower mass flow. The stall margin is enhanced.